I haven't taught kids ESL (just adults) but I used a lot of ESL techniques when I taught my kids things, and judging from that experience, I'd say that you should incorporate English into your play. It seems you could start with numbers, for example, blocks or cards, or things in the home, or colors or food. You can sing songs, Head shoulders knees and toes for example, for parts of the body. You could do things like "Give me the ...." (if you have flashcards). Or "Put your hand on your head." for things to do. You can model "Please" "Thank you" "Excuse me" "Hello" "Good-bye" Just use the same language every week.